fix(admin): 修复三个编辑页 flex 约束和滚动问题

- ActivityEdit.vue、ArticleEdit.vue、ProductEdit.vue 均调整为 flex 布局
- 统一 .edit 根元素、>.el-card 以及 .el-card__body 为 flex + min-height:0
- el-card__body 增加 overflow: hidden，防止卡片内容被裁剪或产生横向滚动
- 与 Layout/admin-tokens 的 .admin-page 弹性约束保持一致，确保长表单可内部滚动

cfc-web/src/views/admin/ActivityEdit.vue

@@ -541,18 +541,27 @@ activityId
 <style scoped>
 .activity-edit {
   padding: 20px;
-  display: block;
-  min-height: auto;
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  min-height: 0;
 }
 .activity-edit > .el-card {
-  display: block;
-  min-height: auto;
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  min-height: 0;
   width: 100%;
 }
 .activity-edit > .el-card /deep/ .el-card__body {
-  display: block;
-  min-height: auto;
-  overflow: visible;
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  min-height: 0;
+  overflow: hidden;
+  padding: 24px;
+  width: 100%;
+  box-sizing: border-box;
 }
 .activity-edit /deep/ .el-form {
   width: 100%;

cfc-web/src/views/admin/ArticleEdit.vue

@@ -810,18 +810,27 @@ onError: (file, err, res) => {
 <style scoped>
 .article-edit {
   padding: 20px;
-  display: block;
-  min-height: auto;
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  min-height: 0;
 }
 .article-edit > .el-card {
-  display: block;
-  min-height: auto;
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  min-height: 0;
   width: 100%;
 }
 .article-edit > .el-card /deep/ .el-card__body {
-  display: block;
-  min-height: auto;
-  overflow: visible;
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  min-height: 0;
+  overflow: hidden;
+  padding: 24px;
+  width: 100%;
+  box-sizing: border-box;
 }
 .article-edit /deep/ .el-form {
   width: 100%;